I think the first person subjunctive form of that word would be pesque..
But I can't think of a way that it would be used very often.
Edit:
When you do the subjunctive, you usually change the ending (if it ends in -ar, then it switches to an -e form) for the first person.
It's the tense that's used like, "It's possible that I'll fish" or something.
es posible que yo pesque..
I dunno...
[Edited on 9/25/2005]